In conditions of crowded air traffic and/or low visibility, it is necessary that the pilot of one aircraft be warned of the presence of a nearby aircraft so that he may maneuver his aircraft to avoid a disastrous collision. Systems known as TCAS (Traffic Alert and Collision Avoidance System) employ an interrogator mounted on a commercial jet aircraft and transponders carried by each aircraft it is likely to encounter. In this way, an interrogation is communicated by secondary radar between the aircraft carrying TCAS and other threat aircraft in the vicinity. This is done so that an enhanced radar signal is returned to the TCAS-equipped aircraft to enable its pilot to avoid a collision. The transponder also encodes the returned radar signal with information unique to the threat aircraft on which it is installed. With TCAS, the burden is on the pilot of the TCAS-equipped aircraft to avoid a collision when an alert is received.
These systems however are very complicated and very costly and are used primarily on large commercial aircraft and required on all aircraft with more than 31 seats operating in the United States. Because of their high cost, these systems are rarely incorporated on smaller, general aviation aircraft, even when they are flying under adverse weather and traffic conditions; a situation which often leads to a collision hazard. General aviation pilots primarily rely on the “see and avoid” practice for collision avoidance and are often even reluctant to incur the cost of installing a transponder without gaining a direct collision avoidance benefit.
Presently, most unmanned aerial vehicles (UAVs) rely on operations in military restricted airspace to avoid the potential of collision with civilian aircraft. Planned operations in unrestricted portions of the National Airspace System require the ability to “see and avoid” all other air traffic; the same as for manned aircraft. Present air traffic control and TCAS type airborne systems cannot protect UAVs from non-cooperative (i.e., non-transponder equipped) aircraft collision threats. Also there is no present capability for the operator to detect a potential hazard and correct for a potential collision except to keep it in sight from the ground or from a manned chase plane. A primary radar system could provide an equivalent or better “sense and avoid” capability for these aircraft. Further, marine vehicles could also benefit from a system that detects and avoids potential hazards both small (i.e., buoys, logs, etc.) and large (i.e., other ships).
What is needed in the art is a low cost, reliable, collision avoidance system that is particularly useful to protect against a wide variety of non-cooperative vehicles.